Given that I'm at the COP21 U.N. climate conference, the subject of our encounter was climate change. Gates, the billionaire nerd-turned-humanitarian, and founder of Microsoft, announced this week an investment partnership to help bring billions to clean energy research.

I only had time to ask Gates one question before his handlers swept him away.

John D. Sutter

I decided to give that question to one of you -- specifically Jay, one of my followers on Snapchat. (I'm jdsutter on that app). Here's what I asked on Jay's behalf: What one technology on the horizon do you think will help us beat the 2 degrees Celsius target for global warming?

That temperature increase, as I'm sure you know if you've been following this series, is the agreed-upon point at which climate change gets especially catastrophic. It's so important that beating the goal is why more than 140 world leaders gathered here in France to try to figure out how to avoid that level of warming, measured as an increase since the Industrial Revolution. Diplomats will be here at the U.N. COP21 talks at least until December 11.

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Here's how Gates responded to Jay's climate question:

"No single technology (will solve climate change). I think we have to go after fusion and fission and biofuels. I'll mention one that is still in an early stage and very risky -- and that's taking the sun and directly making fuels. And even though it may not work, there's some labs, particularly at Caltech, professor (Nathan) Lewis, who have made some progress on that. It's magical because if you can make the liquid hydrocarbon, the gasoline-type substance, you can always store that and move it around. We know how to do that. So you avoid this storage intermittency problem that's really the toughest thing right now about wind and solar."

The whole thing seemed so cool and collected, delivered in that I'm-the-person-who-can-see-the-future-and-it's-going-to-be-great manner only Bill Gates can pull off. Cool, calm. Gentle, and with a knowing, warm smile.

But here's a little secret: Once the Gates glow faded, I realized I had no idea what he was talking about. Using the sun to create a liquid fuel, like oil? I'd never heard of that.

I stopped a few well-informed people on the street here at COP21 and felt a little better about myself when I realized none of them had heard of this idea either.

Luckily, Gates had referenced a researcher -- Nathan Lewis from the California Institute of Technology. And I managed to track Lewis down via Skype.

CNN's John Sutter speaks with Bill Gates at the climate change conference.

Basically, he told me, he's trying to re-engineer the leaf of a plant. He's turned leaves into multilayer black sheets of plastic -- "imagine a high-performance rain jacket" -- that trap the sun's energy and, through a series of reactions, turn it into a liquid fuel.

"It's just a fuel like any other fuel -- like oil or gas," he said.

"The simplest application involves a kind of club sandwich of cells: a series of catalysts separated by a membrane, and surrounded by light-absorbing material on the top and bottom," Bill Gates wrote last month. "These cells use sunlight to generate enough energy to split water, producing oxygen and hydrogen gas; the hydrogen can be used directly as fuel or in commercial processes like making fertilizer.

"Another approach uses water, carbon dioxide, and sunlight to create hydrocarbons -- making it possible to produce and burn fuels with no net gain or loss of carbon dioxide in the atmosphere."

"We have test pieces of plastic that can be rolled out that do demonstrate this is possible," Lewis told me, adding that it will likely be four or five years before a working prototype exists, and some time beyond that before anything could be deployed on a commercial scale. ("The first iPhone is not the one we hold in our hands now, and the first cell phone was not an iPhone," he said).

He does imagine this happening, though, and has estimated that you could power the United States with this technology if we covered 1% of our land with these plastic, energy-making tarps.

"It's like we're drawing to an inside straight" in poker, hesaid. "We have the middle cards and we need the low or we need the high. There are various ways to be successful. ... We need to keep our options open in order to develop this system."

If it works, Lewis will have solved a major problem in energy efficiency technology: transmission. Solar panels are getting much cheaper, and wind power is expanding, but the energy from those clean sources is difficult to store and/or transmit through the power grid. When the wind isn't blowing or the sun isn't shining, we need backup fuels, such as oil or natural gas, which are among the high-carbon energy sources that are creating global warming, but are easily transported by pipeline.

I hope he succeeds, although I don't think we can wait to expand the use of already-available clean energy technologies we have on the market. I recently visited Denmark, which gets 40% of its electricity from wind, so there's promise in what we already have. To meet the 2 degrees Celsius goal, though, we basically need to ditch fossil fuels completely sometime around midcentury. So big, long-term bets on research make lots of sense, too.

The multibillion-dollar fund Gates announced here at COP21 -- which will pool resources from private investors as well as the governments of 20 countries, including the United States, China and India, as CNN Money reports -- is a massive step in the right direction.

Oh, and by the way, Lewis wasn't at all surprised Gates called him out by name -- and it doesn't make him feel added pressure to succeed.

"It's no pressure at all for us. We're working as hard as we can every day to try to figure out how to bring this thing to life. It's wonderful people are pointing it out," he said.